题解 | #按之字形顺序打印二叉树#

二叉树广度遍历变种，遍历顺序不变，打印顺序变更即可。

import java.util.*;

/*
public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}
*/
import java.util.*;
public class Solution {
    public ArrayList<ArrayList<Integer> > Print(TreeNode pRoot) {
        ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();
        if (pRoot == null) {
            return result;
        }
//         Queue<TreeNode> queue = new ArrayDeque<>();
        List<TreeNode> list = new ArrayList<>();
        list.add(pRoot);
        boolean rev = true;
        while (!list.isEmpty()) {
            ArrayList<Integer> inner = new ArrayList<>();
            int size = list.size();
            for (int i = 0; i < size; i++) {
                TreeNode tmp = list.remove(0);
                if (tmp.left != null) {
                    list.add(tmp.left);
                }
                if (tmp.right != null) {
                    list.add(tmp.right);
                }
                //反向打印
                if (!rev) {
                    inner.add(0, tmp.val);
                } else {
                    inner.add(tmp.val);
                }

            }
            rev = !rev;
            result.add(inner);

        }
        return result;
    }
}